1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) apparatus, and more particularly to a backlight driving apparatus of an LCD apparatus and method for driving the same that are adaptive for automatically shielding a voltage supply upon generation of an error during an operation of lamps.
2. Discussion of the Related Art
Generally, liquid crystal display (LCD) apparatus control the light transmittance of liquid crystal cells in accordance with video signals to display images. Active matrix type LCD apparatus are advantageous for implementation of moving images because a switching device actively controls each liquid crystal cell. A thin film transistor (hereinafter, referred to as “TFT”) is mainly employed for the switching device in active matrix type LCD apparatus.
FIG. 1 is an equivalent circuit diagram of a pixel of an LCD apparatus according to the related art.
Referring to FIG. 1, the LCD converts a digital input data into an analog data voltage on the basis of a gamma reference voltage to supply it to a data line DL and, at the same time, supplies a scanning pulse to a gate line GL to thereby charge a liquid crystal cell Clc.
A gate electrode of the TFT is connected to the gate line GL while a source electrode thereof is connected to the data line DL. Further, a drain electrode of the TFT is connected to a pixel electrode of the liquid crystal cell Clc and to one electrode of a storage capacitor Cst.
A common electrode of the liquid crystal cell Clc is supplied with a common voltage Vcom. The storage capacitor Cst stores a data voltage fed from the data line DL when the TFT is turned on to maintain the data voltage for the liquid crystal cell Clc.
When the scanning pulse is applied to the gate line GL, the TFT is turned on to provide a channel between the source electrode and the drain electrode thereof, thereby supplying a data voltage on the data line DL to the pixel electrode of the liquid crystal cell Clc. The alignment of the liquid crystal molecules of the liquid crystal cell changes in accordance with an electric field generated between the pixel electrode and the common electrode and light incident to the LCD apparatus can thus be modulated to display images.
A configuration of an LCD apparatus according to the related art will now be described. FIG. 2 is a block diagram illustrating a configuration of an LCD apparatus according to the related art.
Referring to FIG. 2, the LCD apparatus 100 includes an LCD panel 110 provided with a thin film transistor (TFT) located adjacent to each crossing of data lines DL1 to DLm and gate lines GL1 to GLn for each liquid crystal cell Clc, a data driver 120 for supplying data voltages to the data lines DL1 to DLm, a gate driver 130 for supplying scanning pulses to the gate lines GL1 to GLn, a gamma reference voltage generator 140 for generating gamma reference voltages and supplying them to the data driver 120, a backlight assembly 150 for irradiating light onto the LCD panel 110, an inverter 160 for applying AC voltages and currents to the backlight assembly 150, a common voltage generator 170 for generating a common voltage Vcom and supplying it to the common electrode of the liquid crystal cell Clc, a gate driving voltage generator 180 for generating a gate high voltage VGH and a gate low voltage VGL and supplying them to the gate driver 130, and a timing controller 190 for controlling the data driver 120 and the gate driver 130.
The LCD panel 110 has a liquid crystal between two glass substrates. On the lower glass substrate of the LCD panel 110, the data lines DL1 to DLm and the gate lines GL1 to GLn perpendicularly cross each other. The TFTs are provided adjacent to crossings of the data lines DL1 to DLm and the gate lines GL1 to GLn. The TFTs supply data voltages from the data lines DL1 to DLm to the liquid crystal cells Clc in response to the scanning pulses. The gate electrodes of the TFTs are connected to the gate lines GL1 to GLn while the source electrodes thereof are connected to the data lines DL1 to DLm. Further, the drain electrodes of the TFTs are connected to the pixel electrodes of the liquid crystal cells Clc and to the storage capacitors Cst.
The TFTs are turned on in response to the scanning pulses applied to the gate terminal thereof via the gate lines GL1 to GLn. Upon turning-on of the TFTs, data voltages on the data lines DL1 to DLm are supplied to the pixel electrodes of the liquid crystal cells Clc.
The data driver 120 supplies data voltages to the data lines DL1 to DLm in response to a data driving control signal DDC from the timing controller 190. Further, the data driver 120 samples and latches digital video data RGB fed from the timing controller 190, converts them into analog data voltages capable of expressing gray scale levels at the liquid crystal cells Clc on the basis of gamma reference voltages generated from the gamma reference voltage generator 140, and then supplies them to the data lines DL1 to DLm.
The gate driver 130 sequentially generates scanning pulses (gate pulses) in response to a gate driving control signal GDC and a gate shift clock GSC from the timing controller 190 and supplies them to the gate lines GL1 to GLn. The gate driver 130 determines a high-level voltage and a low-level voltage of the scanning pulses in accordance with the gate high voltage VGH and the gate low voltage VGL from the gate driving voltage generator 180.
The gamma reference voltage generator 140 receives a highest-level power voltage VDD to generate positive and negative gamma reference voltages and outputs them to the data driver 120.
The backlight assembly 150 is provided at the rear side of the LCD panel 110 and radiates light toward the LCD panel 110 by alternating current AC voltages and currents supplied from the inverter 160.
The inverter 160 converts a rectangular wave signal generated at the interior thereof into a triangular wave signal, compares the triangular wave signal with a direct current DC power voltage VCC supplied from the LCD apparatus, and then generates a burst dimming signal based on the result of the comparison. In response to the burst dimming signal, a driving integrated circuit IC (not shown) in the inverter 160 controls the AC voltages and currents supplied to the backlight assembly 150.
The common voltage generator 170 receives a high-level power voltage VDD to generate a common voltage Vcom, and supplies it to the common electrode of the liquid crystal cell Clc provided at each pixel of the LCD panel 110.
The gate driving voltage generator 180 is supplied with a high-level power voltage VDD to generate the gate high voltage VGH and the gate low voltage VGL, and supplies them to the data driver 130. Herein, the gate high voltage VGH is greater than the threshold voltage of the TFT provided at each pixel of the LCD panel 110 and the gate low voltage VGL is less then the threshold voltage of the TFT. The gate high voltage VGH and the gate low voltage VGL generated in this manner are used for determining a high-level voltage and a low-level voltage of the scanning pulses generated by the gate driver 130, respectively.
The timing controller 190 supplies digital video data RGB from a digital video card (not shown) to the data driver 120 and, at the same time, generates a data driving control signal DCC and a gate driving control signal GDC using horizontal/vertical synchronizing signals H and V in response to a clock signal CLK to supply them to the data driver 120 and the gate driver 130, respectively. Herein, the data driving control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polarity control signal POL and a source output enable signal SOE, etc. The gate driving control signal GDC includes a gate start pulse GSP and a gate output enable signal GOE, etc.
A configuration of the related art backlight driving apparatus included in a backlight assembly of an LCD apparatus having the above-mentioned configuration will now be described.
FIG. 3 is a block diagram illustrating a configuration of a backlight driving apparatus of an LCD apparatus according to the related art.
Referring to FIG. 3, the backlight driving apparatus 200 includes a lamp driving controller 202, a master driver 203, a slave driver 204, a master AC/DC switching portion 205, a slave AC/DC switching portion 206, a master trans 207 and a slave trans 208.
The lamp driving controller 202 generates a push-pull gate signal for controlling a plurality of lamps 201 in accordance with the burst dimming signal.
The master driver 203 and the slave driver 204 generate a pull-bridge gate signal for the plurality of lamps 201 in response to the push-pull gate signal.
The master DC/AC switching portion 205 switches converts a DC high-level voltage DC 400V inputted from the master driver 203 in accordance with the pull-bridge gate signal to an AC voltage 400 Vrms, and supplies a positive AC voltage 400 Vrms and a negative AC voltage 400 Vrms to the master trans 207 via each two signal lines.
The slave DC/AC switching portion 206 converts a DC high-level voltage DC 400V inputted from the slave driver 204 in accordance with the pull-bridge gate signal to an AC voltage 400 Vrms, and supplies a positive AC voltage 400 Vrms and a negative AC voltage 400 Vrms to the slave trans 208 via each two signal paths. The master DC/AC switching portion 205 and the slave DC/AC switching portion 206 output the AC voltages 400 Vrms having the same phase.
The master trans 207 boosts the AC voltage 400 Vrms inputted, via two signal lines, from the master DC/AC switching portion 205 to an AC voltage 750 Vrms and supplies it to an edge of the plurality of lamps 201. The slave trans 208 boosts the AC voltage 400 Vrms inputted, via two signal lines, from the slave DC/AC switching portion 206 to an AC voltage 750 Vrms and supplies it to the other edge of the plurality of lamps 201. The AC voltage 750 Vrms outputted from the slave trans 206 has an adverse phase to the AC voltage 750 Vrms outputted from the master trans 207.
Thus, the AC voltages 750 Vrms having adverse phases are supplied to the both edges of the plurality of lamps 201. As a result, the AC voltage 1500 Vrms is substantially supplied to the plurality of lamps 201. The magnitude of the AC voltage supplied to the lamps 201 may change depending upon the type and number of the lamps.
As described above, the related art backlight driving apparatus does not have an error detection function so that an inspector or customer may be subject to an electrical shock.